The use of various salts of tetrafluoroboric acid have been used to cure or catalyze epoxy resin systems. See, for example U.S. Pat. Nos. 4,379,908 and 4,396,754.
Application and formulation problems still exist with these systems such as handling and nonuniform and inconsistent cures.
It has now been discovered that the active catalyst in such systems appears to be the free tetrafluoroboric acid (HBF.sub.4) and not the salts per se. Accordingly, a fast-setting, low temperature curing epoxy resin adhesive system has been developed which cures with catalytic quantities of HBF.sub.4.